The present invention relates generally to video signal, speed-change reproducing systems, and more particularly to a video signal, speed-change reproducing systems for reproducing a video signal recorded on mutually adjacent tracks with a first pair of alternately active heads having mutually different azimuth angles. The tape travels at a speed which is different from the speed used for making the recording. The recorded signal is reproduced by a second pair of reproducing heads each of which has the same azimuth angle, which may be the same as the azimuth angle of either one of the first pair of heads.
The prior art employs a system wherein a video signal is recorded on a magnetic tape on parallel tracks formed obliquely to the longitudinal direction of the magnetic tape. This tape either stops or travels at a tape speed which is differrent from that used at the time of recording, thereby to carry out speed-change reproduction such as quick-motion reproduction, slow-motion reproduction, or still picture reproduction. In this system, the tape speed at the time of reproduction is different from that at the time of recording. Therefore the path (track) on the tape on which the head traces during reproduction is different from the path (track) traced by the head during recording.
On the one hand, a conventional video signal recording and reproducing system, ordinarily, forms tracks on a recording medium in a manner which leaves an unrecorded zone or band called a guard band between neighboring tracks in order to prevent the generation of beats caused by the reproduced signals of neighboring tracks due to tracking deviation of the head at the time of reproduction. When a tape recorded in this manner is played back by speed-change reproduction as described above, the head traces over the track and the unrecorded band. When the head traces over the unrecorded band, the level of the reproduced signal is remarkably lowered or it disappears completely. For this reason, noise is generated in the reproduced picture. Furthermore, in the above mentioned system, since unrecorded bands are provided between tracks, the utilization efficiency of the tape has been poor.
In addition, there has been a system wherein the angle of inclination of the tape is varied relative to the head rotating plane, in accordance with the tape speed. The heads will then trace accurately over the track at the time of speed-change reproduction. However, this system has been accompanied by problems relating to the complexity of the mechanism for varying the inclination angle of the tape. The complexity gives rise to high cost apparatus, and creates a difficulty of accurate tracking in actual practice.
On the other hand, the assignee of the present invention has previously developed a system wherein tracks are formed on a tape without gaps to guard bands between neighboring tracks. Moreover, a color video signal can be recorded and reproduced on such a tape without the occurrence of an interference beat disturbance. This system is described in U.S. patent application Ser. No. 731,935, now U.S. Pat. No. 4,178,606, entitled "Color video signal recording and/or reproducing system" filed Oct. 13, 1976, and assigned to the assignee of this application, now U.S. Pat. No. 4,178,606, issued Dec. 11, 1979. In this previously developed system, a pair of azimuth heads have gaps which are inclined with a certain azimuth angle, in mutually opposite directions with respect to a direction perpendicular to the longitudinal direction which is of the track. Neighboring tracks are formed in contiguous contact side-by-side without a gap or guard band therebetween. The phase of the chrominance signal is shifted by 90 degrees for every horizontal scanning period. The direction of this phase shifting is reversed from one track to the next neighboring track. In accordance with this system, the tape utilization efficiency is high since the tracks are in close contact with each other. Moreover, there is no beat disturbance.
In this developed system, if the tape speed is merely varied at will in order to carry out speed-change reproduction, a noise component due to a decreasing of the reproduced signal level accompanying tracking deviation will appear at irregular positions on the reproduced picture screen. For this reason, the noise part in the picture moves, and the S/N ratio of the entire picture becomes poor. Consequently, a speed-change reproduced picture cannot be obtained in good picture quality.
In order to remove the above described disadvantages, a new system has been described in U.S. patent application Ser. No. 58,537 entitled "Video Signal, Speed-Change Reproducing System" which is a continuaton-in-part of U.S. patent application Ser. No. 891,409, now abandoned. According to this system, and similarly according to the present invention, noise due to decreasing of the reproduced signal level does not fluctuate and appears at a constant position in the reproduced picture screen (preferably at the vertical blanking position), whereby the above described disadvantages are removed.
However, according to this system, the level of the reproduced signal at a level minimum position nearly assumes zero, whereby the signal is scarcely reproduced. Accordingly, the signal to noise ratio of the parts of the reproduced signal, having a minimum level, is greatly deteriorated. In a case where the minimum reproduced signal level portion is set at the vertical blanking position, the vertical synchronizing signal is not reproduced positively in a good signal to noise ratio, whereby there arises a problem wherein the vertical synchronization is scarcely attained.
In order to remove the above described disadvantages, a further new system is shown in U.S. patent application Ser. No. 58,818 entitled "Video Signal, Speed-Change Reproducing System" which is a continuation-in-part application of U.S. patent application Ser. No. 892,147, now abandoned. According to this system, since head having mutually different azimuth angles and different track widths, signal reproduction can be carried out to a degree such that the reproduced signal level does not become zero. The vertical synchronizing signal is reproduced even when the reproduced signal level becomes a minimum. In accordance with this system, the vertical synchronization can be positively obtained even when a noise bar is produced due to the minimum reproduced signal level, within a vertical blanking period.
However, even with this system, there has been a problem in that noise bars are conspicuous because the reproduced signal level is low in the minimum level part of the reproduced signal.
Furthermore, a more substantial problem is that, particularly at the time of reproduction of a still picture, a pair of heads of mutually different azimuth angles respectively scan helically across two or three tracks and respectively reproduce signals of tracks recorded by heads of the same azimuth angle as the heads carrying out reproduction scanning. Accordingly, even when the tape is not traveling, a reproduced signal of one track and a reproduced signal of a track adjacent thereto are alternately obtained from the pair of heads. Ordinarily, a video signal for one field is recorded along each track. For this reason, the video signals of two fields are reproduced alternately for one field at a time.
However, in the case where the information content of the recorded video signal is that of an image of rapid movement, the information signal of the video signal differs slightly for every field. For this reason, when a reproduced signal obtained as described above by reproducing the video signals of two fields alternately for one field at a time is reproduced as a still picture, the parts of rapid movement do not become completely still and give rise to a problem in that the picture image becomes one wherein there are minute oscillations such as flickers.